﻿/*
 * wepoll - epoll for Windows
 * https://github.com/piscisaureus/wepoll
 *
 * Copyright 2012-2020, Bert Belder <bertbelder@gmail.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *   * Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef WEPOLL_EXPORT
#define WEPOLL_EXPORT
#endif

#include <stdint.h>

enum EPOLL_EVENTS {
    EPOLLIN = (int)(1U << 0),
    EPOLLPRI = (int)(1U << 1),
    EPOLLOUT = (int)(1U << 2),
    EPOLLERR = (int)(1U << 3),
    EPOLLHUP = (int)(1U << 4),
    EPOLLRDNORM = (int)(1U << 6),
    EPOLLRDBAND = (int)(1U << 7),
    EPOLLWRNORM = (int)(1U << 8),
    EPOLLWRBAND = (int)(1U << 9),
    EPOLLMSG = (int)(1U << 10), /* Never reported. */
    EPOLLRDHUP = (int)(1U << 13),
    EPOLLONESHOT = (int)(1U << 31)
};

#define EPOLLIN (1U << 0)
#define EPOLLPRI (1U << 1)
#define EPOLLOUT (1U << 2)
#define EPOLLERR (1U << 3)
#define EPOLLHUP (1U << 4)
#define EPOLLRDNORM (1U << 6)
#define EPOLLRDBAND (1U << 7)
#define EPOLLWRNORM (1U << 8)
#define EPOLLWRBAND (1U << 9)
#define EPOLLMSG (1U << 10)
#define EPOLLRDHUP (1U << 13)
#define EPOLLONESHOT (1U << 31)

#define EPOLL_CTL_ADD 1
#define EPOLL_CTL_MOD 2
#define EPOLL_CTL_DEL 3

typedef void *HANDLE;
typedef uintptr_t SOCKET;

typedef union epoll_data {
    void *ptr;
    int fd;
    uint32_t u32;
    uint64_t u64;
    SOCKET sock; /* Windows specific */
    HANDLE hnd; /* Windows specific */
} epoll_data_t;

struct epoll_event {
    uint32_t events; /* Epoll events and flags */
    epoll_data_t data; /* User data variable */
};

#ifdef __cplusplus
extern "C" {
#endif

WEPOLL_EXPORT HANDLE epoll_create(int size);
WEPOLL_EXPORT HANDLE epoll_create1(int flags);

WEPOLL_EXPORT int epoll_close(HANDLE ephnd);

WEPOLL_EXPORT int epoll_ctl(HANDLE ephnd, int op, SOCKET sock, struct epoll_event *event);

WEPOLL_EXPORT int epoll_wait(HANDLE ephnd, struct epoll_event *events, int maxevents, int timeout);

#ifdef __cplusplus
} /* extern "C" */
#endif

#include <assert.h>

#include <stdlib.h>

#define WEPOLL_INTERNAL static
#define WEPOLL_INTERNAL_EXTERN static

#if defined(__clang__)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wnonportable-system-include-path"
#pragma clang diagnostic ignored "-Wreserved-id-macro"
#elif defined(_MSC_VER)
#pragma warning(push, 1)
#endif

#undef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN

#undef _WIN32_WINNT
#define _WIN32_WINNT 0x0600

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>

#if defined(__clang__)
#pragma clang diagnostic pop
#elif defined(_MSC_VER)
#pragma warning(pop)
#endif

WEPOLL_INTERNAL int nt_global_init(void);

typedef LONG NTSTATUS;
typedef NTSTATUS *PNTSTATUS;

#ifndef NT_SUCCESS
#define NT_SUCCESS(status) (((NTSTATUS)(status)) >= 0)
#endif

#ifndef STATUS_SUCCESS
#define STATUS_SUCCESS ((NTSTATUS)0x00000000L)
#endif

#ifndef STATUS_PENDING
#define STATUS_PENDING ((NTSTATUS)0x00000103L)
#endif

#ifndef STATUS_CANCELLED
#define STATUS_CANCELLED ((NTSTATUS)0xC0000120L)
#endif

#ifndef STATUS_NOT_FOUND
#define STATUS_NOT_FOUND ((NTSTATUS)0xC0000225L)
#endif

typedef struct _IO_STATUS_BLOCK {
    NTSTATUS Status;
    ULONG_PTR Information;
} IO_STATUS_BLOCK, *PIO_STATUS_BLOCK;

typedef VOID(NTAPI *PIO_APC_ROUTINE)(PVOID ApcContext, PIO_STATUS_BLOCK IoStatusBlock, ULONG Reserved);

typedef struct _UNICODE_STRING {
    USHORT Length;
    USHORT MaximumLength;
    PWSTR Buffer;
} UNICODE_STRING, *PUNICODE_STRING;

#define RTL_CONSTANT_STRING(s)                                                                                         \
    { sizeof(s) - sizeof((s)[0]), sizeof(s), s }

typedef struct _OBJECT_ATTRIBUTES {
    ULONG Length;
    HANDLE RootDirectory;
    PUNICODE_STRING ObjectName;
    ULONG Attributes;
    PVOID SecurityDescriptor;
    PVOID SecurityQualityOfService;
} OBJECT_ATTRIBUTES, *POBJECT_ATTRIBUTES;

#define RTL_CONSTANT_OBJECT_ATTRIBUTES(ObjectName, Attributes)                                                         \
    { sizeof(OBJECT_ATTRIBUTES), NULL, ObjectName, Attributes, NULL, NULL }

#ifndef FILE_OPEN
#define FILE_OPEN 0x00000001UL
#endif

#define KEYEDEVENT_WAIT 0x00000001UL
#define KEYEDEVENT_WAKE 0x00000002UL
#define KEYEDEVENT_ALL_ACCESS (STANDARD_RIGHTS_REQUIRED | KEYEDEVENT_WAIT | KEYEDEVENT_WAKE)

#define NT_NTDLL_IMPORT_LIST(X)                                                                                        \
    X(NTSTATUS, NTAPI, NtCancelIoFileEx,                                                                               \
      (HANDLE FileHandle, PIO_STATUS_BLOCK IoRequestToCancel, PIO_STATUS_BLOCK IoStatusBlock))                         \
                                                                                                                       \
    X(NTSTATUS, NTAPI, NtCreateFile,                                                                                   \
      (PHANDLE FileHandle, ACCESS_MASK DesiredAccess, POBJECT_ATTRIBUTES ObjectAttributes,                             \
       PIO_STATUS_BLOCK IoStatusBlock, PLARGE_INTEGER AllocationSize, ULONG FileAttributes, ULONG ShareAccess,         \
       ULONG CreateDisposition, ULONG CreateOptions, PVOID EaBuffer, ULONG EaLength))                                  \
                                                                                                                       \
    X(NTSTATUS, NTAPI, NtCreateKeyedEvent,                                                                             \
      (PHANDLE KeyedEventHandle, ACCESS_MASK DesiredAccess, POBJECT_ATTRIBUTES ObjectAttributes, ULONG Flags))         \
                                                                                                                       \
    X(NTSTATUS, NTAPI, NtDeviceIoControlFile,                                                                          \
      (HANDLE FileHandle, HANDLE Event, PIO_APC_ROUTINE ApcRoutine, PVOID ApcContext, PIO_STATUS_BLOCK IoStatusBlock,  \
       ULONG IoControlCode, PVOID InputBuffer, ULONG InputBufferLength, PVOID OutputBuffer, ULONG OutputBufferLength)) \
                                                                                                                       \
    X(NTSTATUS, NTAPI, NtReleaseKeyedEvent,                                                                            \
      (HANDLE KeyedEventHandle, PVOID KeyValue, BOOLEAN Alertable, PLARGE_INTEGER Timeout))                            \
                                                                                                                       \
    X(NTSTATUS, NTAPI, NtWaitForKeyedEvent,                                                                            \
      (HANDLE KeyedEventHandle, PVOID KeyValue, BOOLEAN Alertable, PLARGE_INTEGER Timeout))                            \
                                                                                                                       \
    X(ULONG, WINAPI, RtlNtStatusToDosError, (NTSTATUS Status))

#define X(return_type, attributes, name, parameters) WEPOLL_INTERNAL_EXTERN return_type(attributes *name) parameters;
NT_NTDLL_IMPORT_LIST(X)
#undef X

#define AFD_POLL_RECEIVE 0x0001
#define AFD_POLL_RECEIVE_EXPEDITED 0x0002
#define AFD_POLL_SEND 0x0004
#define AFD_POLL_DISCONNECT 0x0008
#define AFD_POLL_ABORT 0x0010
#define AFD_POLL_LOCAL_CLOSE 0x0020
#define AFD_POLL_ACCEPT 0x0080
#define AFD_POLL_CONNECT_FAIL 0x0100

typedef struct _AFD_POLL_HANDLE_INFO {
    HANDLE Handle;
    ULONG Events;
    NTSTATUS Status;
} AFD_POLL_HANDLE_INFO, *PAFD_POLL_HANDLE_INFO;

typedef struct _AFD_POLL_INFO {
    LARGE_INTEGER Timeout;
    ULONG NumberOfHandles;
    ULONG Exclusive;
    AFD_POLL_HANDLE_INFO Handles[1];
} AFD_POLL_INFO, *PAFD_POLL_INFO;

WEPOLL_INTERNAL int afd_create_device_handle(HANDLE iocp_handle, HANDLE *afd_device_handle_out);

WEPOLL_INTERNAL int afd_poll(HANDLE afd_device_handle, AFD_POLL_INFO *poll_info, IO_STATUS_BLOCK *io_status_block);
WEPOLL_INTERNAL int afd_cancel_poll(HANDLE afd_device_handle, IO_STATUS_BLOCK *io_status_block);

#define return_map_error(value)                                                                                        \
    do {                                                                                                               \
        err_map_win_error();                                                                                           \
        return (value);                                                                                                \
    } while (0)

#define return_set_error(value, error)                                                                                 \
    do {                                                                                                               \
        err_set_win_error(error);                                                                                      \
        return (value);                                                                                                \
    } while (0)

WEPOLL_INTERNAL void err_map_win_error(void);
WEPOLL_INTERNAL void err_set_win_error(DWORD error);
WEPOLL_INTERNAL int err_check_handle(HANDLE handle);

#define IOCTL_AFD_POLL 0x00012024

static UNICODE_STRING afd__device_name = RTL_CONSTANT_STRING(L"\\Device\\Afd\\Wepoll");

static OBJECT_ATTRIBUTES afd__device_attributes = RTL_CONSTANT_OBJECT_ATTRIBUTES(&afd__device_name, 0);

int afd_create_device_handle(HANDLE iocp_handle, HANDLE *afd_device_handle_out) {
    HANDLE afd_device_handle;
    IO_STATUS_BLOCK iosb;
    NTSTATUS status;

    /* By opening \Device\Afd without specifying any extended attributes, we'll
     * get a handle that lets us talk to the AFD driver, but that doesn't have an
     * associated endpoint (so it's not a socket). */
    status = NtCreateFile(
        &afd_device_handle, SYNCHRONIZE, &afd__device_attributes, &iosb, NULL, 0, FILE_SHARE_READ | FILE_SHARE_WRITE,
        FILE_OPEN, 0, NULL, 0);
    if (status != STATUS_SUCCESS)
        return_set_error(-1, RtlNtStatusToDosError(status));

    if (CreateIoCompletionPort(afd_device_handle, iocp_handle, 0, 0) == NULL)
        goto error;

    if (!SetFileCompletionNotificationModes(afd_device_handle, FILE_SKIP_SET_EVENT_ON_HANDLE))
        goto error;

    *afd_device_handle_out = afd_device_handle;
    return 0;

error:
    CloseHandle(afd_device_handle);
    return_map_error(-1);
}

int afd_poll(HANDLE afd_device_handle, AFD_POLL_INFO *poll_info, IO_STATUS_BLOCK *io_status_block) {
    NTSTATUS status;

    /* Blocking operation is not supported. */
    assert(io_status_block != NULL);

    io_status_block->Status = STATUS_PENDING;
    status = NtDeviceIoControlFile(
        afd_device_handle, NULL, NULL, io_status_block, io_status_block, IOCTL_AFD_POLL, poll_info, sizeof *poll_info,
        poll_info, sizeof *poll_info);

    if (status == STATUS_SUCCESS)
        return 0;
    else if (status == STATUS_PENDING)
        return_set_error(-1, ERROR_IO_PENDING);
    else
        return_set_error(-1, RtlNtStatusToDosError(status));
}

int afd_cancel_poll(HANDLE afd_device_handle, IO_STATUS_BLOCK *io_status_block) {
    NTSTATUS cancel_status;
    IO_STATUS_BLOCK cancel_iosb;

    /* If the poll operation has already completed or has been cancelled earlier,
     * there's nothing left for us to do. */
    if (io_status_block->Status != STATUS_PENDING)
        return 0;

    cancel_status = NtCancelIoFileEx(afd_device_handle, io_status_block, &cancel_iosb);

    /* NtCancelIoFileEx() may return STATUS_NOT_FOUND if the operation completed
     * just before calling NtCancelIoFileEx(). This is not an error. */
    if (cancel_status == STATUS_SUCCESS || cancel_status == STATUS_NOT_FOUND)
        return 0;
    else
        return_set_error(-1, RtlNtStatusToDosError(cancel_status));
}

WEPOLL_INTERNAL int epoll_global_init(void);

WEPOLL_INTERNAL int init(void);

typedef struct port_state port_state_t;
typedef struct queue queue_t;
typedef struct sock_state sock_state_t;
typedef struct ts_tree_node ts_tree_node_t;

WEPOLL_INTERNAL port_state_t *port_new(HANDLE *iocp_handle_out);
WEPOLL_INTERNAL int port_close(port_state_t *port_state);
WEPOLL_INTERNAL int port_delete(port_state_t *port_state);

WEPOLL_INTERNAL int port_wait(port_state_t *port_state, struct epoll_event *events, int maxevents, int timeout);

WEPOLL_INTERNAL int port_ctl(port_state_t *port_state, int op, SOCKET sock, struct epoll_event *ev);

WEPOLL_INTERNAL int port_register_socket(port_state_t *port_state, sock_state_t *sock_state, SOCKET socket);
WEPOLL_INTERNAL void port_unregister_socket(port_state_t *port_state, sock_state_t *sock_state);
WEPOLL_INTERNAL sock_state_t *port_find_socket(port_state_t *port_state, SOCKET socket);

WEPOLL_INTERNAL void port_request_socket_update(port_state_t *port_state, sock_state_t *sock_state);
WEPOLL_INTERNAL void port_cancel_socket_update(port_state_t *port_state, sock_state_t *sock_state);

WEPOLL_INTERNAL void port_add_deleted_socket(port_state_t *port_state, sock_state_t *sock_state);
WEPOLL_INTERNAL void port_remove_deleted_socket(port_state_t *port_state, sock_state_t *sock_state);

WEPOLL_INTERNAL HANDLE port_get_iocp_handle(port_state_t *port_state);
WEPOLL_INTERNAL queue_t *port_get_poll_group_queue(port_state_t *port_state);

WEPOLL_INTERNAL port_state_t *port_state_from_handle_tree_node(ts_tree_node_t *tree_node);
WEPOLL_INTERNAL ts_tree_node_t *port_state_to_handle_tree_node(port_state_t *port_state);

/* The reflock is a special kind of lock that normally prevents a chunk of
 * memory from being freed, but does allow the chunk of memory to eventually be
 * released in a coordinated fashion.
 *
 * Under normal operation, threads increase and decrease the reference count,
 * which are wait-free operations.
 *
 * Exactly once during the reflock's lifecycle, a thread holding a reference to
 * the lock may "destroy" the lock; this operation blocks until all other
 * threads holding a reference to the lock have dereferenced it. After
 * "destroy" returns, the calling thread may assume that no other threads have
 * a reference to the lock.
 *
 * Attemmpting to lock or destroy a lock after reflock_unref_and_destroy() has
 * been called is invalid and results in undefined behavior. Therefore the user
 * should use another lock to guarantee that this can't happen.
 */

typedef struct reflock {
    volatile long state; /* 32-bit Interlocked APIs operate on `long` values. */
} reflock_t;

WEPOLL_INTERNAL int reflock_global_init(void);

WEPOLL_INTERNAL void reflock_init(reflock_t *reflock);
WEPOLL_INTERNAL void reflock_ref(reflock_t *reflock);
WEPOLL_INTERNAL void reflock_unref(reflock_t *reflock);
WEPOLL_INTERNAL void reflock_unref_and_destroy(reflock_t *reflock);

#include <stdbool.h>

/* N.b.: the tree functions do not set errno or LastError when they fail. Each
 * of the API functions has at most one failure mode. It is up to the caller to
 * set an appropriate error code when necessary. */

typedef struct tree tree_t;
typedef struct tree_node tree_node_t;

typedef struct tree {
    tree_node_t *root;
} tree_t;

typedef struct tree_node {
    tree_node_t *left;
    tree_node_t *right;
    tree_node_t *parent;
    uintptr_t key;
    bool red;
} tree_node_t;

WEPOLL_INTERNAL void tree_init(tree_t *tree);
WEPOLL_INTERNAL void tree_node_init(tree_node_t *node);

WEPOLL_INTERNAL int tree_add(tree_t *tree, tree_node_t *node, uintptr_t key);
WEPOLL_INTERNAL void tree_del(tree_t *tree, tree_node_t *node);

WEPOLL_INTERNAL tree_node_t *tree_find(const tree_t *tree, uintptr_t key);
WEPOLL_INTERNAL tree_node_t *tree_root(const tree_t *tree);

typedef struct ts_tree {
    tree_t tree;
    SRWLOCK lock;
} ts_tree_t;

typedef struct ts_tree_node {
    tree_node_t tree_node;
    reflock_t reflock;
} ts_tree_node_t;

WEPOLL_INTERNAL void ts_tree_init(ts_tree_t *rtl);
WEPOLL_INTERNAL void ts_tree_node_init(ts_tree_node_t *node);

WEPOLL_INTERNAL int ts_tree_add(ts_tree_t *ts_tree, ts_tree_node_t *node, uintptr_t key);

WEPOLL_INTERNAL ts_tree_node_t *ts_tree_del_and_ref(ts_tree_t *ts_tree, uintptr_t key);
WEPOLL_INTERNAL ts_tree_node_t *ts_tree_find_and_ref(ts_tree_t *ts_tree, uintptr_t key);

WEPOLL_INTERNAL void ts_tree_node_unref(ts_tree_node_t *node);
WEPOLL_INTERNAL void ts_tree_node_unref_and_destroy(ts_tree_node_t *node);

static ts_tree_t epoll__handle_tree;

int epoll_global_init(void) {
    ts_tree_init(&epoll__handle_tree);
    return 0;
}

static HANDLE epoll__create(void) {
    port_state_t *port_state;
    HANDLE ephnd;
    ts_tree_node_t *tree_node;

    if (init() < 0)
        return NULL;

    port_state = port_new(&ephnd);
    if (port_state == NULL)
        return NULL;

    tree_node = port_state_to_handle_tree_node(port_state);
    if (ts_tree_add(&epoll__handle_tree, tree_node, (uintptr_t)ephnd) < 0) {
        /* This should never happen. */
        port_delete(port_state);
        return_set_error(NULL, ERROR_ALREADY_EXISTS);
    }

    return ephnd;
}

HANDLE epoll_create(int size) {
    if (size <= 0)
        return_set_error(NULL, ERROR_INVALID_PARAMETER);

    return epoll__create();
}

HANDLE epoll_create1(int flags) {
    if (flags != 0)
        return_set_error(NULL, ERROR_INVALID_PARAMETER);

    return epoll__create();
}

int epoll_close(HANDLE ephnd) {
    ts_tree_node_t *tree_node;
    port_state_t *port_state;

    if (init() < 0)
        return -1;

    tree_node = ts_tree_del_and_ref(&epoll__handle_tree, (uintptr_t)ephnd);
    if (tree_node == NULL) {
        err_set_win_error(ERROR_INVALID_PARAMETER);
        goto err;
    }

    port_state = port_state_from_handle_tree_node(tree_node);
    port_close(port_state);

    ts_tree_node_unref_and_destroy(tree_node);

    return port_delete(port_state);

err:
    err_check_handle(ephnd);
    return -1;
}

int epoll_ctl(HANDLE ephnd, int op, SOCKET sock, struct epoll_event *ev) {
    ts_tree_node_t *tree_node;
    port_state_t *port_state;
    int r;

    if (init() < 0)
        return -1;

    tree_node = ts_tree_find_and_ref(&epoll__handle_tree, (uintptr_t)ephnd);
    if (tree_node == NULL) {
        err_set_win_error(ERROR_INVALID_PARAMETER);
        goto err;
    }

    port_state = port_state_from_handle_tree_node(tree_node);
    r = port_ctl(port_state, op, sock, ev);

    ts_tree_node_unref(tree_node);

    if (r < 0)
        goto err;

    return 0;

err:
    /* On Linux, in the case of epoll_ctl(), EBADF takes priority over other
     * errors. Wepoll mimics this behavior. */
    err_check_handle(ephnd);
    err_check_handle((HANDLE)sock);
    return -1;
}

int epoll_wait(HANDLE ephnd, struct epoll_event *events, int maxevents, int timeout) {
    ts_tree_node_t *tree_node;
    port_state_t *port_state;
    int num_events;

    if (maxevents <= 0)
        return_set_error(-1, ERROR_INVALID_PARAMETER);

    if (init() < 0)
        return -1;

    tree_node = ts_tree_find_and_ref(&epoll__handle_tree, (uintptr_t)ephnd);
    if (tree_node == NULL) {
        err_set_win_error(ERROR_INVALID_PARAMETER);
        goto err;
    }

    port_state = port_state_from_handle_tree_node(tree_node);
    num_events = port_wait(port_state, events, maxevents, timeout);

    ts_tree_node_unref(tree_node);

    if (num_events < 0)
        goto err;

    return num_events;

err:
    err_check_handle(ephnd);
    return -1;
}

#include <errno.h>

#define ERR__ERRNO_MAPPINGS(X)                                                                                         \
    X(ERROR_ACCESS_DENIED, EACCES)                                                                                     \
    X(ERROR_ALREADY_EXISTS, EEXIST)                                                                                    \
    X(ERROR_BAD_COMMAND, EACCES)                                                                                       \
    X(ERROR_BAD_EXE_FORMAT, ENOEXEC)                                                                                   \
    X(ERROR_BAD_LENGTH, EACCES)                                                                                        \
    X(ERROR_BAD_NETPATH, ENOENT)                                                                                       \
    X(ERROR_BAD_NET_NAME, ENOENT)                                                                                      \
    X(ERROR_BAD_NET_RESP, ENETDOWN)                                                                                    \
    X(ERROR_BAD_PATHNAME, ENOENT)                                                                                      \
    X(ERROR_BROKEN_PIPE, EPIPE)                                                                                        \
    X(ERROR_CANNOT_MAKE, EACCES)                                                                                       \
    X(ERROR_COMMITMENT_LIMIT, ENOMEM)                                                                                  \
    X(ERROR_CONNECTION_ABORTED, ECONNABORTED)                                                                          \
    X(ERROR_CONNECTION_ACTIVE, EISCONN)                                                                                \
    X(ERROR_CONNECTION_REFUSED, ECONNREFUSED)                                                                          \
    X(ERROR_CRC, EACCES)                                                                                               \
    X(ERROR_DIR_NOT_EMPTY, ENOTEMPTY)                                                                                  \
    X(ERROR_DISK_FULL, ENOSPC)                                                                                         \
    X(ERROR_DUP_NAME, EADDRINUSE)                                                                                      \
    X(ERROR_FILENAME_EXCED_RANGE, ENOENT)                                                                              \
    X(ERROR_FILE_NOT_FOUND, ENOENT)                                                                                    \
    X(ERROR_GEN_FAILURE, EACCES)                                                                                       \
    X(ERROR_GRACEFUL_DISCONNECT, EPIPE)                                                                                \
    X(ERROR_HOST_DOWN, EHOSTUNREACH)                                                                                   \
    X(ERROR_HOST_UNREACHABLE, EHOSTUNREACH)                                                                            \
    X(ERROR_INSUFFICIENT_BUFFER, EFAULT)                                                                               \
    X(ERROR_INVALID_ADDRESS, EADDRNOTAVAIL)                                                                            \
    X(ERROR_INVALID_FUNCTION, EINVAL)                                                                                  \
    X(ERROR_INVALID_HANDLE, EBADF)                                                                                     \
    X(ERROR_INVALID_NETNAME, EADDRNOTAVAIL)                                                                            \
    X(ERROR_INVALID_PARAMETER, EINVAL)                                                                                 \
    X(ERROR_INVALID_USER_BUFFER, EMSGSIZE)                                                                             \
    X(ERROR_IO_PENDING, EINPROGRESS)                                                                                   \
    X(ERROR_LOCK_VIOLATION, EACCES)                                                                                    \
    X(ERROR_MORE_DATA, EMSGSIZE)                                                                                       \
    X(ERROR_NETNAME_DELETED, ECONNABORTED)                                                                             \
    X(ERROR_NETWORK_ACCESS_DENIED, EACCES)                                                                             \
    X(ERROR_NETWORK_BUSY, ENETDOWN)                                                                                    \
    X(ERROR_NETWORK_UNREACHABLE, ENETUNREACH)                                                                          \
    X(ERROR_NOACCESS, EFAULT)                                                                                          \
    X(ERROR_NONPAGED_SYSTEM_RESOURCES, ENOMEM)                                                                         \
    X(ERROR_NOT_ENOUGH_MEMORY, ENOMEM)                                                                                 \
    X(ERROR_NOT_ENOUGH_QUOTA, ENOMEM)                                                                                  \
    X(ERROR_NOT_FOUND, ENOENT)                                                                                         \
    X(ERROR_NOT_LOCKED, EACCES)                                                                                        \
    X(ERROR_NOT_READY, EACCES)                                                                                         \
    X(ERROR_NOT_SAME_DEVICE, EXDEV)                                                                                    \
    X(ERROR_NOT_SUPPORTED, ENOTSUP)                                                                                    \
    X(ERROR_NO_MORE_FILES, ENOENT)                                                                                     \
    X(ERROR_NO_SYSTEM_RESOURCES, ENOMEM)                                                                               \
    X(ERROR_OPERATION_ABORTED, EINTR)                                                                                  \
    X(ERROR_OUT_OF_PAPER, EACCES)                                                                                      \
    X(ERROR_PAGED_SYSTEM_RESOURCES, ENOMEM)                                                                            \
    X(ERROR_PAGEFILE_QUOTA, ENOMEM)                                                                                    \
    X(ERROR_PATH_NOT_FOUND, ENOENT)                                                                                    \
    X(ERROR_PIPE_NOT_CONNECTED, EPIPE)                                                                                 \
    X(ERROR_PORT_UNREACHABLE, ECONNRESET)                                                                              \
    X(ERROR_PROTOCOL_UNREACHABLE, ENETUNREACH)                                                                         \
    X(ERROR_REM_NOT_LIST, ECONNREFUSED)                                                                                \
    X(ERROR_REQUEST_ABORTED, EINTR)                                                                                    \
    X(ERROR_REQ_NOT_ACCEP, EWOULDBLOCK)                                                                                \
    X(ERROR_SECTOR_NOT_FOUND, EACCES)                                                                                  \
    X(ERROR_SEM_TIMEOUT, ETIMEDOUT)                                                                                    \
    X(ERROR_SHARING_VIOLATION, EACCES)                                                                                 \
    X(ERROR_TOO_MANY_NAMES, ENOMEM)                                                                                    \
    X(ERROR_TOO_MANY_OPEN_FILES, EMFILE)                                                                               \
    X(ERROR_UNEXP_NET_ERR, ECONNABORTED)                                                                               \
    X(ERROR_WAIT_NO_CHILDREN, ECHILD)                                                                                  \
    X(ERROR_WORKING_SET_QUOTA, ENOMEM)                                                                                 \
    X(ERROR_WRITE_PROTECT, EACCES)                                                                                     \
    X(ERROR_WRONG_DISK, EACCES)                                                                                        \
    X(WSAEACCES, EACCES)                                                                                               \
    X(WSAEADDRINUSE, EADDRINUSE)                                                                                       \
    X(WSAEADDRNOTAVAIL, EADDRNOTAVAIL)                                                                                 \
    X(WSAEAFNOSUPPORT, EAFNOSUPPORT)                                                                                   \
    X(WSAECONNABORTED, ECONNABORTED)                                                                                   \
    X(WSAECONNREFUSED, ECONNREFUSED)                                                                                   \
    X(WSAECONNRESET, ECONNRESET)                                                                                       \
    X(WSAEDISCON, EPIPE)                                                                                               \
    X(WSAEFAULT, EFAULT)                                                                                               \
    X(WSAEHOSTDOWN, EHOSTUNREACH)                                                                                      \
    X(WSAEHOSTUNREACH, EHOSTUNREACH)                                                                                   \
    X(WSAEINPROGRESS, EBUSY)                                                                                           \
    X(WSAEINTR, EINTR)                                                                                                 \
    X(WSAEINVAL, EINVAL)                                                                                               \
    X(WSAEISCONN, EISCONN)                                                                                             \
    X(WSAEMSGSIZE, EMSGSIZE)                                                                                           \
    X(WSAENETDOWN, ENETDOWN)                                                                                           \
    X(WSAENETRESET, EHOSTUNREACH)                                                                                      \
    X(WSAENETUNREACH, ENETUNREACH)                                                                                     \
    X(WSAENOBUFS, ENOMEM)                                                                                              \
    X(WSAENOTCONN, ENOTCONN)                                                                                           \
    X(WSAENOTSOCK, ENOTSOCK)                                                                                           \
    X(WSAEOPNOTSUPP, EOPNOTSUPP)                                                                                       \
    X(WSAEPROCLIM, ENOMEM)                                                                                             \
    X(WSAESHUTDOWN, EPIPE)                                                                                             \
    X(WSAETIMEDOUT, ETIMEDOUT)                                                                                         \
    X(WSAEWOULDBLOCK, EWOULDBLOCK)                                                                                     \
    X(WSANOTINITIALISED, ENETDOWN)                                                                                     \
    X(WSASYSNOTREADY, ENETDOWN)                                                                                        \
    X(WSAVERNOTSUPPORTED, ENOSYS)

static errno_t err__map_win_error_to_errno(DWORD error) {
    switch (error) {
#define X(error_sym, errno_sym)                                                                                        \
    case error_sym: return errno_sym;
        ERR__ERRNO_MAPPINGS(X)
#undef X
    }
    return EINVAL;
}

void err_map_win_error(void) {
    errno = err__map_win_error_to_errno(GetLastError());
}

void err_set_win_error(DWORD error) {
    SetLastError(error);
    errno = err__map_win_error_to_errno(error);
}

int err_check_handle(HANDLE handle) {
    DWORD flags;

    /* GetHandleInformation() succeeds when passed INVALID_HANDLE_VALUE, so check
     * for this condition explicitly. */
    if (handle == INVALID_HANDLE_VALUE)
        return_set_error(-1, ERROR_INVALID_HANDLE);

    if (!GetHandleInformation(handle, &flags))
        return_map_error(-1);

    return 0;
}

#include <stddef.h>

#define array_count(a) (sizeof(a) / (sizeof((a)[0])))

#define container_of(ptr, type, member) ((type *)((uintptr_t)(ptr)-offsetof(type, member)))

#define unused_var(v) ((void)(v))

/* Polyfill `inline` for older versions of msvc (up to Visual Studio 2013) */
#if defined(_MSC_VER) && _MSC_VER < 1900
#define inline __inline
#endif

WEPOLL_INTERNAL int ws_global_init(void);
WEPOLL_INTERNAL SOCKET ws_get_base_socket(SOCKET socket);

static bool init__done = false;
static INIT_ONCE init__once = INIT_ONCE_STATIC_INIT;

static BOOL CALLBACK init__once_callback(INIT_ONCE *once, void *parameter, void **context) {
    unused_var(once);
    unused_var(parameter);
    unused_var(context);

    /* N.b. that initialization order matters here. */
    if (ws_global_init() < 0 || nt_global_init() < 0 || reflock_global_init() < 0 || epoll_global_init() < 0)
        return FALSE;

    init__done = true;
    return TRUE;
}

int init(void) {
    if (!init__done && !InitOnceExecuteOnce(&init__once, init__once_callback, NULL, NULL))
        /* `InitOnceExecuteOnce()` itself is infallible, and it doesn't set any
         * error code when the once-callback returns FALSE. We return -1 here to
         * indicate that global initialization failed; the failing init function is
         * resposible for setting `errno` and calling `SetLastError()`. */
        return -1;

    return 0;
}

/* Set up a workaround for the following problem:
 *   FARPROC addr = GetProcAddress(...);
 *   MY_FUNC func = (MY_FUNC) addr;          <-- GCC 8 warning/error.
 *   MY_FUNC func = (MY_FUNC) (void*) addr;  <-- MSVC  warning/error.
 * To compile cleanly with either compiler, do casts with this "bridge" type:
 *   MY_FUNC func = (MY_FUNC) (nt__fn_ptr_cast_t) addr; */
#ifdef __GNUC__
typedef void *nt__fn_ptr_cast_t;
#else
typedef FARPROC nt__fn_ptr_cast_t;
#endif

#define X(return_type, attributes, name, parameters) WEPOLL_INTERNAL return_type(attributes *name) parameters = NULL;
NT_NTDLL_IMPORT_LIST(X)
#undef X

int nt_global_init(void) {
    HMODULE ntdll;
    FARPROC fn_ptr;

    ntdll = GetModuleHandleW(L"ntdll.dll");
    if (ntdll == NULL)
        return -1;

#define X(return_type, attributes, name, parameters)                                                                   \
    fn_ptr = GetProcAddress(ntdll, #name);                                                                             \
    if (fn_ptr == NULL)                                                                                                \
        return -1;                                                                                                     \
    name = (return_type(attributes *) parameters)(nt__fn_ptr_cast_t)fn_ptr;
    NT_NTDLL_IMPORT_LIST(X)
#undef X

    return 0;
}

#include <string.h>

typedef struct poll_group poll_group_t;

typedef struct queue_node queue_node_t;

WEPOLL_INTERNAL poll_group_t *poll_group_acquire(port_state_t *port);
WEPOLL_INTERNAL void poll_group_release(poll_group_t *poll_group);

WEPOLL_INTERNAL void poll_group_delete(poll_group_t *poll_group);

WEPOLL_INTERNAL poll_group_t *poll_group_from_queue_node(queue_node_t *queue_node);
WEPOLL_INTERNAL HANDLE poll_group_get_afd_device_handle(poll_group_t *poll_group);

typedef struct queue_node {
    queue_node_t *prev;
    queue_node_t *next;
} queue_node_t;

typedef struct queue {
    queue_node_t head;
} queue_t;

WEPOLL_INTERNAL void queue_init(queue_t *queue);
WEPOLL_INTERNAL void queue_node_init(queue_node_t *node);

WEPOLL_INTERNAL queue_node_t *queue_first(const queue_t *queue);
WEPOLL_INTERNAL queue_node_t *queue_last(const queue_t *queue);

WEPOLL_INTERNAL void queue_prepend(queue_t *queue, queue_node_t *node);
WEPOLL_INTERNAL void queue_append(queue_t *queue, queue_node_t *node);
WEPOLL_INTERNAL void queue_move_to_start(queue_t *queue, queue_node_t *node);
WEPOLL_INTERNAL void queue_move_to_end(queue_t *queue, queue_node_t *node);
WEPOLL_INTERNAL void queue_remove(queue_node_t *node);

WEPOLL_INTERNAL bool queue_is_empty(const queue_t *queue);
WEPOLL_INTERNAL bool queue_is_enqueued(const queue_node_t *node);

#define POLL_GROUP__MAX_GROUP_SIZE 32

typedef struct poll_group {
    port_state_t *port_state;
    queue_node_t queue_node;
    HANDLE afd_device_handle;
    size_t group_size;
} poll_group_t;

static poll_group_t *poll_group__new(port_state_t *port_state) {
    HANDLE iocp_handle = port_get_iocp_handle(port_state);
    queue_t *poll_group_queue = port_get_poll_group_queue(port_state);

    poll_group_t *poll_group = malloc(sizeof *poll_group);
    if (poll_group == NULL)
        return_set_error(NULL, ERROR_NOT_ENOUGH_MEMORY);

    memset(poll_group, 0, sizeof *poll_group);

    queue_node_init(&poll_group->queue_node);
    poll_group->port_state = port_state;

    if (afd_create_device_handle(iocp_handle, &poll_group->afd_device_handle) < 0) {
        free(poll_group);
        return NULL;
    }

    queue_append(poll_group_queue, &poll_group->queue_node);

    return poll_group;
}

void poll_group_delete(poll_group_t *poll_group) {
    assert(poll_group->group_size == 0);
    CloseHandle(poll_group->afd_device_handle);
    queue_remove(&poll_group->queue_node);
    free(poll_group);
}

poll_group_t *poll_group_from_queue_node(queue_node_t *queue_node) {
    return container_of(queue_node, poll_group_t, queue_node);
}

HANDLE poll_group_get_afd_device_handle(poll_group_t *poll_group) {
    return poll_group->afd_device_handle;
}

poll_group_t *poll_group_acquire(port_state_t *port_state) {
    queue_t *poll_group_queue = port_get_poll_group_queue(port_state);
    poll_group_t *poll_group = !queue_is_empty(poll_group_queue)
        ? container_of(queue_last(poll_group_queue), poll_group_t, queue_node)
        : NULL;

    if (poll_group == NULL || poll_group->group_size >= POLL_GROUP__MAX_GROUP_SIZE)
        poll_group = poll_group__new(port_state);
    if (poll_group == NULL)
        return NULL;

    if (++poll_group->group_size == POLL_GROUP__MAX_GROUP_SIZE)
        queue_move_to_start(poll_group_queue, &poll_group->queue_node);

    return poll_group;
}

void poll_group_release(poll_group_t *poll_group) {
    port_state_t *port_state = poll_group->port_state;
    queue_t *poll_group_queue = port_get_poll_group_queue(port_state);

    poll_group->group_size--;
    assert(poll_group->group_size < POLL_GROUP__MAX_GROUP_SIZE);

    queue_move_to_end(poll_group_queue, &poll_group->queue_node);

    /* Poll groups are currently only freed when the epoll port is closed. */
}

WEPOLL_INTERNAL sock_state_t *sock_new(port_state_t *port_state, SOCKET socket);
WEPOLL_INTERNAL void sock_delete(port_state_t *port_state, sock_state_t *sock_state);
WEPOLL_INTERNAL void sock_force_delete(port_state_t *port_state, sock_state_t *sock_state);

WEPOLL_INTERNAL int sock_set_event(port_state_t *port_state, sock_state_t *sock_state, const struct epoll_event *ev);

WEPOLL_INTERNAL int sock_update(port_state_t *port_state, sock_state_t *sock_state);
WEPOLL_INTERNAL int sock_feed_event(port_state_t *port_state, IO_STATUS_BLOCK *io_status_block, struct epoll_event *ev);

WEPOLL_INTERNAL sock_state_t *sock_state_from_queue_node(queue_node_t *queue_node);
WEPOLL_INTERNAL queue_node_t *sock_state_to_queue_node(sock_state_t *sock_state);
WEPOLL_INTERNAL sock_state_t *sock_state_from_tree_node(tree_node_t *tree_node);
WEPOLL_INTERNAL tree_node_t *sock_state_to_tree_node(sock_state_t *sock_state);

#define PORT__MAX_ON_STACK_COMPLETIONS 256

typedef struct port_state {
    HANDLE iocp_handle;
    tree_t sock_tree;
    queue_t sock_update_queue;
    queue_t sock_deleted_queue;
    queue_t poll_group_queue;
    ts_tree_node_t handle_tree_node;
    CRITICAL_SECTION lock;
    size_t active_poll_count;
} port_state_t;

static inline port_state_t *port__alloc(void) {
    port_state_t *port_state = malloc(sizeof *port_state);
    if (port_state == NULL)
        return_set_error(NULL, ERROR_NOT_ENOUGH_MEMORY);

    return port_state;
}

static inline void port__free(port_state_t *port) {
    assert(port != NULL);
    free(port);
}

static inline HANDLE port__create_iocp(void) {
    HANDLE iocp_handle = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 0);
    if (iocp_handle == NULL)
        return_map_error(NULL);

    return iocp_handle;
}

port_state_t *port_new(HANDLE *iocp_handle_out) {
    port_state_t *port_state;
    HANDLE iocp_handle;

    port_state = port__alloc();
    if (port_state == NULL)
        goto err1;

    iocp_handle = port__create_iocp();
    if (iocp_handle == NULL)
        goto err2;

    memset(port_state, 0, sizeof *port_state);

    port_state->iocp_handle = iocp_handle;
    tree_init(&port_state->sock_tree);
    queue_init(&port_state->sock_update_queue);
    queue_init(&port_state->sock_deleted_queue);
    queue_init(&port_state->poll_group_queue);
    ts_tree_node_init(&port_state->handle_tree_node);
    InitializeCriticalSection(&port_state->lock);

    *iocp_handle_out = iocp_handle;
    return port_state;

err2:
    port__free(port_state);
err1:
    return NULL;
}

static inline int port__close_iocp(port_state_t *port_state) {
    HANDLE iocp_handle = port_state->iocp_handle;
    port_state->iocp_handle = NULL;

    if (!CloseHandle(iocp_handle))
        return_map_error(-1);

    return 0;
}

int port_close(port_state_t *port_state) {
    int result;

    EnterCriticalSection(&port_state->lock);
    result = port__close_iocp(port_state);
    LeaveCriticalSection(&port_state->lock);

    return result;
}

int port_delete(port_state_t *port_state) {
    tree_node_t *tree_node;
    queue_node_t *queue_node;

    /* At this point the IOCP port should have been closed. */
    assert(port_state->iocp_handle == NULL);

    while ((tree_node = tree_root(&port_state->sock_tree)) != NULL) {
        sock_state_t *sock_state = sock_state_from_tree_node(tree_node);
        sock_force_delete(port_state, sock_state);
    }

    while ((queue_node = queue_first(&port_state->sock_deleted_queue)) != NULL) {
        sock_state_t *sock_state = sock_state_from_queue_node(queue_node);
        sock_force_delete(port_state, sock_state);
    }

    while ((queue_node = queue_first(&port_state->poll_group_queue)) != NULL) {
        poll_group_t *poll_group = poll_group_from_queue_node(queue_node);
        poll_group_delete(poll_group);
    }

    assert(queue_is_empty(&port_state->sock_update_queue));

    DeleteCriticalSection(&port_state->lock);

    port__free(port_state);

    return 0;
}

static int port__update_events(port_state_t *port_state) {
    queue_t *sock_update_queue = &port_state->sock_update_queue;

    /* Walk the queue, submitting new poll requests for every socket that needs
     * it. */
    while (!queue_is_empty(sock_update_queue)) {
        queue_node_t *queue_node = queue_first(sock_update_queue);
        sock_state_t *sock_state = sock_state_from_queue_node(queue_node);

        if (sock_update(port_state, sock_state) < 0)
            return -1;

        /* sock_update() removes the socket from the update queue. */
    }

    return 0;
}

static inline void port__update_events_if_polling(port_state_t *port_state) {
    if (port_state->active_poll_count > 0)
        port__update_events(port_state);
}

static inline int port__feed_events(
    port_state_t *port_state, struct epoll_event *epoll_events, OVERLAPPED_ENTRY *iocp_events, DWORD iocp_event_count) {
    int epoll_event_count = 0;
    DWORD i;

    for (i = 0; i < iocp_event_count; i++) {
        IO_STATUS_BLOCK *io_status_block = (IO_STATUS_BLOCK *)iocp_events[i].lpOverlapped;
        struct epoll_event *ev = &epoll_events[epoll_event_count];

        epoll_event_count += sock_feed_event(port_state, io_status_block, ev);
    }

    return epoll_event_count;
}

static inline int port__poll(
    port_state_t *port_state, struct epoll_event *epoll_events, OVERLAPPED_ENTRY *iocp_events, DWORD maxevents,
    DWORD timeout) {
    DWORD completion_count;

    if (port__update_events(port_state) < 0)
        return -1;

    port_state->active_poll_count++;

    LeaveCriticalSection(&port_state->lock);

    BOOL r = GetQueuedCompletionStatusEx(
        port_state->iocp_handle, iocp_events, maxevents, &completion_count, timeout, FALSE);

    EnterCriticalSection(&port_state->lock);

    port_state->active_poll_count--;

    if (!r)
        return_map_error(-1);

    return port__feed_events(port_state, epoll_events, iocp_events, completion_count);
}

int port_wait(port_state_t *port_state, struct epoll_event *events, int maxevents, int timeout) {
    OVERLAPPED_ENTRY stack_iocp_events[PORT__MAX_ON_STACK_COMPLETIONS];
    OVERLAPPED_ENTRY *iocp_events;
    uint64_t due = 0;
    DWORD gqcs_timeout;
    int result;

    /* Check whether `maxevents` is in range. */
    if (maxevents <= 0)
        return_set_error(-1, ERROR_INVALID_PARAMETER);

    /* Decide whether the IOCP completion list can live on the stack, or allocate
     * memory for it on the heap. */
    if ((size_t)maxevents <= array_count(stack_iocp_events)) {
        iocp_events = stack_iocp_events;
    } else if ((iocp_events = malloc((size_t)maxevents * sizeof *iocp_events)) == NULL) {
        iocp_events = stack_iocp_events;
        maxevents = array_count(stack_iocp_events);
    }

    /* Compute the timeout for GetQueuedCompletionStatus, and the wait end
     * time, if the user specified a timeout other than zero or infinite. */
    if (timeout > 0) {
        due = GetTickCount64() + (uint64_t)timeout;
        gqcs_timeout = (DWORD)timeout;
    } else if (timeout == 0) {
        gqcs_timeout = 0;
    } else {
        gqcs_timeout = INFINITE;
    }

    EnterCriticalSection(&port_state->lock);

    /* Dequeue completion packets until either at least one interesting event
     * has been discovered, or the timeout is reached. */
    for (;;) {
        uint64_t now;

        result = port__poll(port_state, events, iocp_events, (DWORD)maxevents, gqcs_timeout);
        if (result < 0 || result > 0)
            break; /* Result, error, or time-out. */

        if (timeout < 0)
            continue; /* When timeout is negative, never time out. */

        /* Update time. */
        now = GetTickCount64();

        /* Do not allow the due time to be in the past. */
        if (now >= due) {
            SetLastError(WAIT_TIMEOUT);
            break;
        }

        /* Recompute time-out argument for GetQueuedCompletionStatus. */
        gqcs_timeout = (DWORD)(due - now);
    }

    port__update_events_if_polling(port_state);

    LeaveCriticalSection(&port_state->lock);

    if (iocp_events != stack_iocp_events)
        free(iocp_events);

    if (result >= 0)
        return result;
    else if (GetLastError() == WAIT_TIMEOUT)
        return 0;
    else
        return -1;
}

static inline int port__ctl_add(port_state_t *port_state, SOCKET sock, struct epoll_event *ev) {
    sock_state_t *sock_state = sock_new(port_state, sock);
    if (sock_state == NULL)
        return -1;

    if (sock_set_event(port_state, sock_state, ev) < 0) {
        sock_delete(port_state, sock_state);
        return -1;
    }

    port__update_events_if_polling(port_state);

    return 0;
}

static inline int port__ctl_mod(port_state_t *port_state, SOCKET sock, struct epoll_event *ev) {
    sock_state_t *sock_state = port_find_socket(port_state, sock);
    if (sock_state == NULL)
        return -1;

    if (sock_set_event(port_state, sock_state, ev) < 0)
        return -1;

    port__update_events_if_polling(port_state);

    return 0;
}

static inline int port__ctl_del(port_state_t *port_state, SOCKET sock) {
    sock_state_t *sock_state = port_find_socket(port_state, sock);
    if (sock_state == NULL)
        return -1;

    sock_delete(port_state, sock_state);

    return 0;
}

static inline int port__ctl_op(port_state_t *port_state, int op, SOCKET sock, struct epoll_event *ev) {
    switch (op) {
        case EPOLL_CTL_ADD: return port__ctl_add(port_state, sock, ev);
        case EPOLL_CTL_MOD: return port__ctl_mod(port_state, sock, ev);
        case EPOLL_CTL_DEL: return port__ctl_del(port_state, sock);
        default: return_set_error(-1, ERROR_INVALID_PARAMETER);
    }
}

int port_ctl(port_state_t *port_state, int op, SOCKET sock, struct epoll_event *ev) {
    int result;

    EnterCriticalSection(&port_state->lock);
    result = port__ctl_op(port_state, op, sock, ev);
    LeaveCriticalSection(&port_state->lock);

    return result;
}

int port_register_socket(port_state_t *port_state, sock_state_t *sock_state, SOCKET socket) {
    if (tree_add(&port_state->sock_tree, sock_state_to_tree_node(sock_state), socket) < 0)
        return_set_error(-1, ERROR_ALREADY_EXISTS);
    return 0;
}

void port_unregister_socket(port_state_t *port_state, sock_state_t *sock_state) {
    tree_del(&port_state->sock_tree, sock_state_to_tree_node(sock_state));
}

sock_state_t *port_find_socket(port_state_t *port_state, SOCKET socket) {
    tree_node_t *tree_node = tree_find(&port_state->sock_tree, socket);
    if (tree_node == NULL)
        return_set_error(NULL, ERROR_NOT_FOUND);
    return sock_state_from_tree_node(tree_node);
}

void port_request_socket_update(port_state_t *port_state, sock_state_t *sock_state) {
    if (queue_is_enqueued(sock_state_to_queue_node(sock_state)))
        return;
    queue_append(&port_state->sock_update_queue, sock_state_to_queue_node(sock_state));
}

void port_cancel_socket_update(port_state_t *port_state, sock_state_t *sock_state) {
    unused_var(port_state);
    if (!queue_is_enqueued(sock_state_to_queue_node(sock_state)))
        return;
    queue_remove(sock_state_to_queue_node(sock_state));
}

void port_add_deleted_socket(port_state_t *port_state, sock_state_t *sock_state) {
    if (queue_is_enqueued(sock_state_to_queue_node(sock_state)))
        return;
    queue_append(&port_state->sock_deleted_queue, sock_state_to_queue_node(sock_state));
}

void port_remove_deleted_socket(port_state_t *port_state, sock_state_t *sock_state) {
    unused_var(port_state);
    if (!queue_is_enqueued(sock_state_to_queue_node(sock_state)))
        return;
    queue_remove(sock_state_to_queue_node(sock_state));
}

HANDLE port_get_iocp_handle(port_state_t *port_state) {
    assert(port_state->iocp_handle != NULL);
    return port_state->iocp_handle;
}

queue_t *port_get_poll_group_queue(port_state_t *port_state) {
    return &port_state->poll_group_queue;
}

port_state_t *port_state_from_handle_tree_node(ts_tree_node_t *tree_node) {
    return container_of(tree_node, port_state_t, handle_tree_node);
}

ts_tree_node_t *port_state_to_handle_tree_node(port_state_t *port_state) {
    return &port_state->handle_tree_node;
}

void queue_init(queue_t *queue) {
    queue_node_init(&queue->head);
}

void queue_node_init(queue_node_t *node) {
    node->prev = node;
    node->next = node;
}

static inline void queue__detach_node(queue_node_t *node) {
    node->prev->next = node->next;
    node->next->prev = node->prev;
}

queue_node_t *queue_first(const queue_t *queue) {
    return !queue_is_empty(queue) ? queue->head.next : NULL;
}

queue_node_t *queue_last(const queue_t *queue) {
    return !queue_is_empty(queue) ? queue->head.prev : NULL;
}

void queue_prepend(queue_t *queue, queue_node_t *node) {
    node->next = queue->head.next;
    node->prev = &queue->head;
    node->next->prev = node;
    queue->head.next = node;
}

void queue_append(queue_t *queue, queue_node_t *node) {
    node->next = &queue->head;
    node->prev = queue->head.prev;
    node->prev->next = node;
    queue->head.prev = node;
}

void queue_move_to_start(queue_t *queue, queue_node_t *node) {
    queue__detach_node(node);
    queue_prepend(queue, node);
}

void queue_move_to_end(queue_t *queue, queue_node_t *node) {
    queue__detach_node(node);
    queue_append(queue, node);
}

void queue_remove(queue_node_t *node) {
    queue__detach_node(node);
    queue_node_init(node);
}

bool queue_is_empty(const queue_t *queue) {
    return !queue_is_enqueued(&queue->head);
}

bool queue_is_enqueued(const queue_node_t *node) {
    return node->prev != node;
}

#define REFLOCK__REF ((long)0x00000001UL)
#define REFLOCK__REF_MASK ((long)0x0fffffffUL)
#define REFLOCK__DESTROY ((long)0x10000000UL)
#define REFLOCK__DESTROY_MASK ((long)0xf0000000UL)
#define REFLOCK__POISON ((long)0x300dead0UL)

static HANDLE reflock__keyed_event = NULL;

int reflock_global_init(void) {
    NTSTATUS status = NtCreateKeyedEvent(&reflock__keyed_event, KEYEDEVENT_ALL_ACCESS, NULL, 0);
    if (status != STATUS_SUCCESS)
        return_set_error(-1, RtlNtStatusToDosError(status));
    return 0;
}

void reflock_init(reflock_t *reflock) {
    reflock->state = 0;
}

static void reflock__signal_event(void *address) {
    NTSTATUS status = NtReleaseKeyedEvent(reflock__keyed_event, address, FALSE, NULL);
    if (status != STATUS_SUCCESS)
        abort();
}

static void reflock__await_event(void *address) {
    NTSTATUS status = NtWaitForKeyedEvent(reflock__keyed_event, address, FALSE, NULL);
    if (status != STATUS_SUCCESS)
        abort();
}

void reflock_ref(reflock_t *reflock) {
    long state = InterlockedAdd(&reflock->state, REFLOCK__REF);

    /* Verify that the counter didn't overflow and the lock isn't destroyed. */
    assert((state & REFLOCK__DESTROY_MASK) == 0);
    unused_var(state);
}

void reflock_unref(reflock_t *reflock) {
    long state = InterlockedAdd(&reflock->state, -REFLOCK__REF);

    /* Verify that the lock was referenced and not already destroyed. */
    assert((state & REFLOCK__DESTROY_MASK & ~REFLOCK__DESTROY) == 0);

    if (state == REFLOCK__DESTROY)
        reflock__signal_event(reflock);
}

void reflock_unref_and_destroy(reflock_t *reflock) {
    long state = InterlockedAdd(&reflock->state, REFLOCK__DESTROY - REFLOCK__REF);
    long ref_count = state & REFLOCK__REF_MASK;

    /* Verify that the lock was referenced and not already destroyed. */
    assert((state & REFLOCK__DESTROY_MASK) == REFLOCK__DESTROY);

    if (ref_count != 0)
        reflock__await_event(reflock);

    state = InterlockedExchange(&reflock->state, REFLOCK__POISON);
    assert(state == REFLOCK__DESTROY);
}

#define SOCK__KNOWN_EPOLL_EVENTS                                                                                       \
    (EPOLLIN | EPOLLPRI | EPOLLOUT | EPOLLERR | EPOLLHUP | EPOLLRDNORM | EPOLLRDBAND | EPOLLWRNORM | EPOLLWRBAND       \
     | EPOLLMSG | EPOLLRDHUP)

typedef enum sock__poll_status { SOCK__POLL_IDLE = 0, SOCK__POLL_PENDING, SOCK__POLL_CANCELLED } sock__poll_status_t;

typedef struct sock_state {
    IO_STATUS_BLOCK io_status_block;
    AFD_POLL_INFO poll_info;
    queue_node_t queue_node;
    tree_node_t tree_node;
    poll_group_t *poll_group;
    SOCKET base_socket;
    epoll_data_t user_data;
    uint32_t user_events;
    uint32_t pending_events;
    sock__poll_status_t poll_status;
    bool delete_pending;
} sock_state_t;

static inline sock_state_t *sock__alloc(void) {
    sock_state_t *sock_state = malloc(sizeof *sock_state);
    if (sock_state == NULL)
        return_set_error(NULL, ERROR_NOT_ENOUGH_MEMORY);
    return sock_state;
}

static inline void sock__free(sock_state_t *sock_state) {
    assert(sock_state != NULL);
    free(sock_state);
}

static inline int sock__cancel_poll(sock_state_t *sock_state) {
    assert(sock_state->poll_status == SOCK__POLL_PENDING);

    if (afd_cancel_poll(poll_group_get_afd_device_handle(sock_state->poll_group), &sock_state->io_status_block) < 0)
        return -1;

    sock_state->poll_status = SOCK__POLL_CANCELLED;
    sock_state->pending_events = 0;
    return 0;
}

sock_state_t *sock_new(port_state_t *port_state, SOCKET socket) {
    SOCKET base_socket;
    poll_group_t *poll_group;
    sock_state_t *sock_state;

    if (socket == 0 || socket == INVALID_SOCKET)
        return_set_error(NULL, ERROR_INVALID_HANDLE);

    base_socket = ws_get_base_socket(socket);
    if (base_socket == INVALID_SOCKET)
        return NULL;

    poll_group = poll_group_acquire(port_state);
    if (poll_group == NULL)
        return NULL;

    sock_state = sock__alloc();
    if (sock_state == NULL)
        goto err1;

    memset(sock_state, 0, sizeof *sock_state);

    sock_state->base_socket = base_socket;
    sock_state->poll_group = poll_group;

    tree_node_init(&sock_state->tree_node);
    queue_node_init(&sock_state->queue_node);

    if (port_register_socket(port_state, sock_state, socket) < 0)
        goto err2;

    return sock_state;

err2:
    sock__free(sock_state);
err1:
    poll_group_release(poll_group);

    return NULL;
}

static int sock__delete(port_state_t *port_state, sock_state_t *sock_state, bool force) {
    if (!sock_state->delete_pending) {
        if (sock_state->poll_status == SOCK__POLL_PENDING)
            sock__cancel_poll(sock_state);

        port_cancel_socket_update(port_state, sock_state);
        port_unregister_socket(port_state, sock_state);

        sock_state->delete_pending = true;
    }

    /* If the poll request still needs to complete, the sock_state object can't
     * be free()d yet. `sock_feed_event()` or `port_close()` will take care
     * of this later. */
    if (force || sock_state->poll_status == SOCK__POLL_IDLE) {
        /* Free the sock_state now. */
        port_remove_deleted_socket(port_state, sock_state);
        poll_group_release(sock_state->poll_group);
        sock__free(sock_state);
    } else {
        /* Free the socket later. */
        port_add_deleted_socket(port_state, sock_state);
    }

    return 0;
}

void sock_delete(port_state_t *port_state, sock_state_t *sock_state) {
    sock__delete(port_state, sock_state, false);
}

void sock_force_delete(port_state_t *port_state, sock_state_t *sock_state) {
    sock__delete(port_state, sock_state, true);
}

int sock_set_event(port_state_t *port_state, sock_state_t *sock_state, const struct epoll_event *ev) {
    /* EPOLLERR and EPOLLHUP are always reported, even when not requested by the
     * caller. However they are disabled after a event has been reported for a
     * socket for which the EPOLLONESHOT flag was set. */
    uint32_t events = ev->events | EPOLLERR | EPOLLHUP;

    sock_state->user_events = events;
    sock_state->user_data = ev->data;

    if ((events & SOCK__KNOWN_EPOLL_EVENTS & ~sock_state->pending_events) != 0)
        port_request_socket_update(port_state, sock_state);

    return 0;
}

static inline DWORD sock__epoll_events_to_afd_events(uint32_t epoll_events) {
    /* Always monitor for AFD_POLL_LOCAL_CLOSE, which is triggered when the
     * socket is closed with closesocket() or CloseHandle(). */
    DWORD afd_events = AFD_POLL_LOCAL_CLOSE;

    if (epoll_events & (EPOLLIN | EPOLLRDNORM))
        afd_events |= AFD_POLL_RECEIVE | AFD_POLL_ACCEPT;
    if (epoll_events & (EPOLLPRI | EPOLLRDBAND))
        afd_events |= AFD_POLL_RECEIVE_EXPEDITED;
    if (epoll_events & (EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND))
        afd_events |= AFD_POLL_SEND;
    if (epoll_events & (EPOLLIN | EPOLLRDNORM | EPOLLRDHUP))
        afd_events |= AFD_POLL_DISCONNECT;
    if (epoll_events & EPOLLHUP)
        afd_events |= AFD_POLL_ABORT;
    if (epoll_events & EPOLLERR)
        afd_events |= AFD_POLL_CONNECT_FAIL;

    return afd_events;
}

static inline uint32_t sock__afd_events_to_epoll_events(DWORD afd_events) {
    uint32_t epoll_events = 0;

    if (afd_events & (AFD_POLL_RECEIVE | AFD_POLL_ACCEPT))
        epoll_events |= EPOLLIN | EPOLLRDNORM;
    if (afd_events & AFD_POLL_RECEIVE_EXPEDITED)
        epoll_events |= EPOLLPRI | EPOLLRDBAND;
    if (afd_events & AFD_POLL_SEND)
        epoll_events |= EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND;
    if (afd_events & AFD_POLL_DISCONNECT)
        epoll_events |= EPOLLIN | EPOLLRDNORM | EPOLLRDHUP;
    if (afd_events & AFD_POLL_ABORT)
        epoll_events |= EPOLLHUP;
    if (afd_events & AFD_POLL_CONNECT_FAIL)
        /* Linux reports all these events after connect() has failed. */
        epoll_events |= EPOLLIN | EPOLLOUT | EPOLLERR | EPOLLRDNORM | EPOLLWRNORM | EPOLLRDHUP;

    return epoll_events;
}

int sock_update(port_state_t *port_state, sock_state_t *sock_state) {
    assert(!sock_state->delete_pending);

    if ((sock_state->poll_status == SOCK__POLL_PENDING)
        && (sock_state->user_events & SOCK__KNOWN_EPOLL_EVENTS & ~sock_state->pending_events) == 0) {
        /* All the events the user is interested in are already being monitored by
         * the pending poll operation. It might spuriously complete because of an
         * event that we're no longer interested in; when that happens we'll submit
         * a new poll operation with the updated event mask. */

    } else if (sock_state->poll_status == SOCK__POLL_PENDING) {
        /* A poll operation is already pending, but it's not monitoring for all the
         * events that the user is interested in. Therefore, cancel the pending
         * poll operation; when we receive it's completion package, a new poll
         * operation will be submitted with the correct event mask. */
        if (sock__cancel_poll(sock_state) < 0)
            return -1;

    } else if (sock_state->poll_status == SOCK__POLL_CANCELLED) {
        /* The poll operation has already been cancelled, we're still waiting for
         * it to return. For now, there's nothing that needs to be done. */

    } else if (sock_state->poll_status == SOCK__POLL_IDLE) {
        /* No poll operation is pending; start one. */
        sock_state->poll_info.Exclusive = FALSE;
        sock_state->poll_info.NumberOfHandles = 1;
        sock_state->poll_info.Timeout.QuadPart = INT64_MAX;
        sock_state->poll_info.Handles[0].Handle = (HANDLE)sock_state->base_socket;
        sock_state->poll_info.Handles[0].Status = 0;
        sock_state->poll_info.Handles[0].Events = sock__epoll_events_to_afd_events(sock_state->user_events);

        if (afd_poll(
                poll_group_get_afd_device_handle(sock_state->poll_group), &sock_state->poll_info,
                &sock_state->io_status_block)
            < 0) {
            switch (GetLastError()) {
                case ERROR_IO_PENDING:
                    /* Overlapped poll operation in progress; this is expected. */
                    break;
                case ERROR_INVALID_HANDLE:
                    /* Socket closed; it'll be dropped from the epoll set. */
                    return sock__delete(port_state, sock_state, false);
                default:
                    /* Other errors are propagated to the caller. */
                    return_map_error(-1);
            }
        }

        /* The poll request was successfully submitted. */
        sock_state->poll_status = SOCK__POLL_PENDING;
        sock_state->pending_events = sock_state->user_events;

    } else {
        /* Unreachable. */
        assert(false);
    }

    port_cancel_socket_update(port_state, sock_state);
    return 0;
}

int sock_feed_event(port_state_t *port_state, IO_STATUS_BLOCK *io_status_block, struct epoll_event *ev) {
    sock_state_t *sock_state = container_of(io_status_block, sock_state_t, io_status_block);
    AFD_POLL_INFO *poll_info = &sock_state->poll_info;
    uint32_t epoll_events = 0;

    sock_state->poll_status = SOCK__POLL_IDLE;
    sock_state->pending_events = 0;

    if (sock_state->delete_pending) {
        /* Socket has been deleted earlier and can now be freed. */
        return sock__delete(port_state, sock_state, false);

    } else if (io_status_block->Status == STATUS_CANCELLED) {
        /* The poll request was cancelled by CancelIoEx. */

    } else if (!NT_SUCCESS(io_status_block->Status)) {
        /* The overlapped request itself failed in an unexpected way. */
        epoll_events = EPOLLERR;

    } else if (poll_info->NumberOfHandles < 1) {
        /* This poll operation succeeded but didn't report any socket events. */

    } else if (poll_info->Handles[0].Events & AFD_POLL_LOCAL_CLOSE) {
        /* The poll operation reported that the socket was closed. */
        return sock__delete(port_state, sock_state, false);

    } else {
        /* Events related to our socket were reported. */
        epoll_events = sock__afd_events_to_epoll_events(poll_info->Handles[0].Events);
    }

    /* Requeue the socket so a new poll request will be submitted. */
    port_request_socket_update(port_state, sock_state);

    /* Filter out events that the user didn't ask for. */
    epoll_events &= sock_state->user_events;

    /* Return if there are no epoll events to report. */
    if (epoll_events == 0)
        return 0;

    /* If the the socket has the EPOLLONESHOT flag set, unmonitor all events,
     * even EPOLLERR and EPOLLHUP. But always keep looking for closed sockets. */
    if (sock_state->user_events & EPOLLONESHOT)
        sock_state->user_events = 0;

    ev->data = sock_state->user_data;
    ev->events = epoll_events;
    return 1;
}

sock_state_t *sock_state_from_queue_node(queue_node_t *queue_node) {
    return container_of(queue_node, sock_state_t, queue_node);
}

queue_node_t *sock_state_to_queue_node(sock_state_t *sock_state) {
    return &sock_state->queue_node;
}

sock_state_t *sock_state_from_tree_node(tree_node_t *tree_node) {
    return container_of(tree_node, sock_state_t, tree_node);
}

tree_node_t *sock_state_to_tree_node(sock_state_t *sock_state) {
    return &sock_state->tree_node;
}

void ts_tree_init(ts_tree_t *ts_tree) {
    tree_init(&ts_tree->tree);
    InitializeSRWLock(&ts_tree->lock);
}

void ts_tree_node_init(ts_tree_node_t *node) {
    tree_node_init(&node->tree_node);
    reflock_init(&node->reflock);
}

int ts_tree_add(ts_tree_t *ts_tree, ts_tree_node_t *node, uintptr_t key) {
    int r;

    AcquireSRWLockExclusive(&ts_tree->lock);
    r = tree_add(&ts_tree->tree, &node->tree_node, key);
    ReleaseSRWLockExclusive(&ts_tree->lock);

    return r;
}

static inline ts_tree_node_t *ts_tree__find_node(ts_tree_t *ts_tree, uintptr_t key) {
    tree_node_t *tree_node = tree_find(&ts_tree->tree, key);
    if (tree_node == NULL)
        return NULL;

    return container_of(tree_node, ts_tree_node_t, tree_node);
}

ts_tree_node_t *ts_tree_del_and_ref(ts_tree_t *ts_tree, uintptr_t key) {
    ts_tree_node_t *ts_tree_node;

    AcquireSRWLockExclusive(&ts_tree->lock);

    ts_tree_node = ts_tree__find_node(ts_tree, key);
    if (ts_tree_node != NULL) {
        tree_del(&ts_tree->tree, &ts_tree_node->tree_node);
        reflock_ref(&ts_tree_node->reflock);
    }

    ReleaseSRWLockExclusive(&ts_tree->lock);

    return ts_tree_node;
}

ts_tree_node_t *ts_tree_find_and_ref(ts_tree_t *ts_tree, uintptr_t key) {
    ts_tree_node_t *ts_tree_node;

    AcquireSRWLockShared(&ts_tree->lock);

    ts_tree_node = ts_tree__find_node(ts_tree, key);
    if (ts_tree_node != NULL)
        reflock_ref(&ts_tree_node->reflock);

    ReleaseSRWLockShared(&ts_tree->lock);

    return ts_tree_node;
}

void ts_tree_node_unref(ts_tree_node_t *node) {
    reflock_unref(&node->reflock);
}

void ts_tree_node_unref_and_destroy(ts_tree_node_t *node) {
    reflock_unref_and_destroy(&node->reflock);
}

void tree_init(tree_t *tree) {
    memset(tree, 0, sizeof *tree);
}

void tree_node_init(tree_node_t *node) {
    memset(node, 0, sizeof *node);
}

#define TREE__ROTATE(cis, trans)                                                                                       \
    tree_node_t *p = node;                                                                                             \
    tree_node_t *q = node->trans;                                                                                      \
    tree_node_t *parent = p->parent;                                                                                   \
                                                                                                                       \
    if (parent) {                                                                                                      \
        if (parent->left == p)                                                                                         \
            parent->left = q;                                                                                          \
        else                                                                                                           \
            parent->right = q;                                                                                         \
    } else {                                                                                                           \
        tree->root = q;                                                                                                \
    }                                                                                                                  \
                                                                                                                       \
    q->parent = parent;                                                                                                \
    p->parent = q;                                                                                                     \
    p->trans = q->cis;                                                                                                 \
    if (p->trans)                                                                                                      \
        p->trans->parent = p;                                                                                          \
    q->cis = p;

static inline void tree__rotate_left(tree_t *tree, tree_node_t *node) {
    TREE__ROTATE(left, right)
}

static inline void tree__rotate_right(tree_t *tree, tree_node_t *node) {
    TREE__ROTATE(right, left)
}

#define TREE__INSERT_OR_DESCEND(side)                                                                                  \
    if (parent->side) {                                                                                                \
        parent = parent->side;                                                                                         \
    } else {                                                                                                           \
        parent->side = node;                                                                                           \
        break;                                                                                                         \
    }

#define TREE__REBALANCE_AFTER_INSERT(cis, trans)                                                                       \
    tree_node_t *grandparent = parent->parent;                                                                         \
    tree_node_t *uncle = grandparent->trans;                                                                           \
                                                                                                                       \
    if (uncle && uncle->red) {                                                                                         \
        parent->red = uncle->red = false;                                                                              \
        grandparent->red = true;                                                                                       \
        node = grandparent;                                                                                            \
    } else {                                                                                                           \
        if (node == parent->trans) {                                                                                   \
            tree__rotate_##cis(tree, parent);                                                                          \
            node = parent;                                                                                             \
            parent = node->parent;                                                                                     \
        }                                                                                                              \
        parent->red = false;                                                                                           \
        grandparent->red = true;                                                                                       \
        tree__rotate_##trans(tree, grandparent);                                                                       \
    }

int tree_add(tree_t *tree, tree_node_t *node, uintptr_t key) {
    tree_node_t *parent;

    parent = tree->root;
    if (parent) {
        for (;;) {
            if (key < parent->key) {
                TREE__INSERT_OR_DESCEND(left)
            } else if (key > parent->key) {
                TREE__INSERT_OR_DESCEND(right)
            } else {
                return -1;
            }
        }
    } else {
        tree->root = node;
    }

    node->key = key;
    node->left = node->right = NULL;
    node->parent = parent;
    node->red = true;

    for (; parent && parent->red; parent = node->parent) {
        if (parent == parent->parent->left) {
            TREE__REBALANCE_AFTER_INSERT(left, right)
        } else {
            TREE__REBALANCE_AFTER_INSERT(right, left)
        }
    }
    tree->root->red = false;

    return 0;
}

#define TREE__REBALANCE_AFTER_REMOVE(cis, trans)                                                                       \
    tree_node_t *sibling = parent->trans;                                                                              \
                                                                                                                       \
    if (sibling->red) {                                                                                                \
        sibling->red = false;                                                                                          \
        parent->red = true;                                                                                            \
        tree__rotate_##cis(tree, parent);                                                                              \
        sibling = parent->trans;                                                                                       \
    }                                                                                                                  \
    if ((sibling->left && sibling->left->red) || (sibling->right && sibling->right->red)) {                            \
        if (!sibling->trans || !sibling->trans->red) {                                                                 \
            sibling->cis->red = false;                                                                                 \
            sibling->red = true;                                                                                       \
            tree__rotate_##trans(tree, sibling);                                                                       \
            sibling = parent->trans;                                                                                   \
        }                                                                                                              \
        sibling->red = parent->red;                                                                                    \
        parent->red = sibling->trans->red = false;                                                                     \
        tree__rotate_##cis(tree, parent);                                                                              \
        node = tree->root;                                                                                             \
        break;                                                                                                         \
    }                                                                                                                  \
    sibling->red = true;

void tree_del(tree_t *tree, tree_node_t *node) {
    tree_node_t *parent = node->parent;
    tree_node_t *left = node->left;
    tree_node_t *right = node->right;
    tree_node_t *next;
    bool red;

    if (!left) {
        next = right;
    } else if (!right) {
        next = left;
    } else {
        next = right;
        while (next->left)
            next = next->left;
    }

    if (parent) {
        if (parent->left == node)
            parent->left = next;
        else
            parent->right = next;
    } else {
        tree->root = next;
    }

    if (left && right) {
        red = next->red;
        next->red = node->red;
        next->left = left;
        left->parent = next;
        if (next != right) {
            parent = next->parent;
            next->parent = node->parent;
            node = next->right;
            parent->left = node;
            next->right = right;
            right->parent = next;
        } else {
            next->parent = parent;
            parent = next;
            node = next->right;
        }
    } else {
        red = node->red;
        node = next;
    }

    if (node)
        node->parent = parent;
    if (red)
        return;
    if (node && node->red) {
        node->red = false;
        return;
    }

    do {
        if (node == tree->root)
            break;
        if (node == parent->left) {
            TREE__REBALANCE_AFTER_REMOVE(left, right)
        } else {
            TREE__REBALANCE_AFTER_REMOVE(right, left)
        }
        node = parent;
        parent = parent->parent;
    } while (!node->red);

    if (node)
        node->red = false;
}

tree_node_t *tree_find(const tree_t *tree, uintptr_t key) {
    tree_node_t *node = tree->root;
    while (node) {
        if (key < node->key)
            node = node->left;
        else if (key > node->key)
            node = node->right;
        else
            return node;
    }
    return NULL;
}

tree_node_t *tree_root(const tree_t *tree) {
    return tree->root;
}

#ifndef SIO_BSP_HANDLE_POLL
#define SIO_BSP_HANDLE_POLL 0x4800001D
#endif

#ifndef SIO_BASE_HANDLE
#define SIO_BASE_HANDLE 0x48000022
#endif

int ws_global_init(void) {
    int r;
    WSADATA wsa_data;

    r = WSAStartup(MAKEWORD(2, 2), &wsa_data);
    if (r != 0)
        return_set_error(-1, (DWORD)r);

    return 0;
}

static inline SOCKET ws__ioctl_get_bsp_socket(SOCKET socket, DWORD ioctl) {
    SOCKET bsp_socket;
    DWORD bytes;

    if (WSAIoctl(socket, ioctl, NULL, 0, &bsp_socket, sizeof bsp_socket, &bytes, NULL, NULL) != SOCKET_ERROR)
        return bsp_socket;
    else
        return INVALID_SOCKET;
}

SOCKET ws_get_base_socket(SOCKET socket) {
    SOCKET base_socket;
    DWORD error;

    for (;;) {
        base_socket = ws__ioctl_get_bsp_socket(socket, SIO_BASE_HANDLE);
        if (base_socket != INVALID_SOCKET)
            return base_socket;

        error = GetLastError();
        if (error == WSAENOTSOCK)
            return_set_error(INVALID_SOCKET, error);

        /* Even though Microsoft documentation clearly states that LSPs should
         * never intercept the `SIO_BASE_HANDLE` ioctl [1], Komodia based LSPs do
         * so anyway, breaking it, with the apparent intention of preventing LSP
         * bypass [2]. Fortunately they don't handle `SIO_BSP_HANDLE_POLL`, which
         * will at least let us obtain the socket associated with the next winsock
         * protocol chain entry. If this succeeds, loop around and call
         * `SIO_BASE_HANDLE` again with the returned BSP socket, to make sure that
         * we unwrap all layers and retrieve the actual base socket.
         *  [1] https://docs.microsoft.com/en-us/windows/win32/winsock/winsock-ioctls
         *  [2] https://www.komodia.com/newwiki/index.php?title=Komodia%27s_Redirector_bug_fixes#Version_2.2.2.6
         */
        base_socket = ws__ioctl_get_bsp_socket(socket, SIO_BSP_HANDLE_POLL);
        if (base_socket != INVALID_SOCKET && base_socket != socket)
            socket = base_socket;
        else
            return_set_error(INVALID_SOCKET, error);
    }
}
